The use of optical multiplexing and demultiplexing sub-assemblies, and optical modules containing such sub-assemblies, in fiber optic communication systems is well known. Such sub-assemblies and optical modules are generally configured to receive and/transmit optical signals from or to fiber optic cables.
One example of an industry-standard form factor optical module containing such sub-assemblies is the now largely outdated XENPAK module. Due to the need to make optical modules ever smaller, the X2 optical module was recently introduced. The X2 module is configured to house a small form factor LX4 optical sub-assembly that typically supports optical communications at speeds of around 10 Gigabits per second.
The LX4 sub-assembly typically offers a single interface that can transmit or receive over both multimode and single mode optical fibers. The X2 form factor of the LX4 permits modular interconnections to be established, where the X2 module within which the LX4 module is housed is inserted, for example, into a pluggable port slot in a switch, router, server or storage system. The LX4 sub-assembly leverages the technology of wavelength division multiplexing (“WDM”), and permits transmission and reception of multiple signal sources, each at a different wavelength, over the same fiber optic cable.
FIG. 1 shows a block diagram of an exemplary 10 Gigabit LX4 transmitter and receiver system. As shown, a parallel interface known as “XAUI” is employed, as is typical in many 10 Gigabit per second chip-to-chip interfaces. XAUI is built over the physical coding layer (“PCS”) into an XAUI physical layer (“PHY”) that divides the 10 Gigabit per second stream of data into four parallel streams of 2.5 Gigabits per second each which, after 8B/10B coding, are converted into four data streams of 3.125 Gigabits per second each.
In transmitter 100a, four channels are fed into tour lasers, such as distributed feedback (“DFB”) lasers. Each of the four lasers transmits signals at a different wavelength, which typically correspond to 1275 nm, ±6 nm; 1300 nm, ±6 nm; 1325 nm, ±6 nm; and 1350 nm, ±6 nm. These signals are multiplexed together using an optical multiplexer sub-assembly using a technique known as coarse wavelength division multiplexing (“CWDM”) on a single optical fiber.
Receiver 100b comprises a CDWM demultiplexer and four PIN detectors, one for each of the four signals transmitted at a different wavelength. The current generated by each PIN is fed into a transimpedance amplifier (“TIA”), which generates four parallel electrical data streams operating at 3.125 Gigabits per second. The high attenuation associated with the fiber and the optical components typically results in low amplitude output signals being generated by the TIA, and as a result a limiting amplifier (“LA”) follows the output of the TIA.
The four output streams from the LA are fed into an XAUI physical layer (“PHY”) that recovers the clock from the data stream, and aligns the data to compensate for skew introduced between the four data streams arising from the different speeds of each wavelength in the fiber, and encodes them back to 8 bits in the 8B/10B PCS.
FIG. 2 shows a functional block diagram of one type of a 4 channel 10 GBASE-LX4 ROSA Receive Optical Sub-Assembly (“ROSA”) demultiplexer with an integrated photodetector array, as manufactured by Cube Optics AG. Optical demultiplexer 100 comprises a four-channel optical receiver with a high speed PIN photodetector array and four transimpedance amplifiers with limiting function. The LX4 demultiplexer/receiver is designed for use in small form factor X2 transceiver modules with an optical connector receptacle, and has four 100 ohm differential CML RF output signals. In addition, an average optical power monitor signal allows active fiber alignment and a signal modulation detecting function enables loss of signal (“LOS”) for each channel. The receiver requires a 3.3 V single power supply voltage (Vcc).
FIG. 3 shows an exemplary embodiment of X2 form factor optical module 200 that contains an LX4 optical sub-assembly. X2 form factor housing 200 is generally formed of a metal such as a zinc or aluminum alloy, and is typically die-cast. Being electrically conductive and surrounding LX4 sub-assembly 100, X2 form factor housing 200 provides some degree of electromagnetic interference (“EMI”) protection or shielding.
Blaze Network Products, Inc. of Dublin, Calif. (hereafter “Blaze”), now owned by Omron Electronic Components, L.L.C. (hereafter “Omron”), manufactures several types of LX4 ROSAs and TOSAs (“Transmitter Optical Sub-Assemblies”) finding particularly efficacious use in the various embodiments of the present invention, more about which we say below. By way of example, Omron manufactures and sells P1 RX-LX4 ROSAs and P1TX-LX4 TOSAs that may be adapted in accordance with the teachings of the present invention.
Blaze obtained several patents covering various aspects of a ROSA and/or a TOSA comprising various optical components configured to fit together and provide an optical sub-assembly capable of demultiplexing incoming or multiplexing outgoing optical signals of different wavelengths. See, for example, U.S. Pat. Nos. 6,201,908; 6,396,978; 6,456,757; 6,558,046; 6,563,976; and 6,572,278, further details concerning which are set forth below. The foregoing patents are hereby incorporated by reference herein, each in its respective entirety.
ROSAs and TOSAs manufactured by Omron are notable for having one or more important components thereof being constructed from integrally molded components formed of substantially optically transparent or transmissive plastic. Reference is now made to FIGS. 1 and 2 of U.S. Pat. No. 6,201,908, where incoming optical signals 90 are routed first through coupling module 60 (numeral 150 in FIGS. 4(a) through 4(c) hereof) by way of fiber optic cable receptacle 80 (numeral 134 in FIGS. 4(a) through 4(c) hereof) formed in ferrule 83 (numeral 130 in FIGS. 4(a) through 4(c) hereof) and configured to receive a fiber optic connector in therein.
From fiber optic cable receptacle 80 (numeral 134 in FIGS. 4(a) through 4(c) hereof), incoming optical signals 90 are directed through plastic collimating lens 65 in coupling module 60 (numeral 150 in FIGS. 4(a) through 4(c) hereof), and reflected upwardly by reflecting surface 66 towards optical block 20 (numeral 110 in FIGS. 4(a) through 4(c) hereof), which is most preferably formed of optical-grade glass provided by Schott AG of Germany. Reflecting surface 66 is most preferably a Total Internal Reflection (“TIR”) surface or air prism. Reflective coating 85 is disposed on first flat upper surface 21 (numeral 112 in FIGS. 4(a) through 4(c) hereof), and is configured to reflect light incident thereon towards first wavelength filter 41.
Optical signals contained within optical signal 90 having the proper wavelength are permitted to pass through filter 41 for focusing by corresponding aspheric lens 71, and thence detection by an underlying corresponding photodetector. The remaining optical signals are reflected upwardly from filter 41 towards reflective coating 85 and first flat upper surface 21 (numeral 112 in FIGS. 4(a) through 4(c) hereof) for reflection therefrom towards filter 42 and corresponding aspheric lens 72. Light signals having wavelengths corresponding to the pass-band of filter 42 are permitted passage therethrough, while the remaining optical signals are once again directed towards reflective coating 85 and first flat upper surface 21 (numeral 112 in FIGS. 4(a) through 4(c) hereof).
The reflection and selective transmission and filtering of optical signal 90 continues until all the various wavelength components of optical signal 90 have been separated from one another according to wavelength, and have been transmitted through their respective aspheric lenses for detection by an array of photodetectors located beneath coupling module 60 (numeral 130 in FIGS. 4(a) through 4(c) hereof) in a photodetector array assembly (numeral 170 in FIGS. 4(a) through 4(c) hereof).
A substantially optically transparent or transmissive plastic may be employed to form coupling module 60 (numeral 130 in FIGS. 4(a) through 4(c) hereof) using integral molding techniques, and has many advantages, including permitting complex optical components such as precision aspheric lenses and TIR reflecting surfaces such as air prisms to be manufactured at relatively low cost.
There are several disadvantages to such an approach, however. One notable problem that has been discovered in the use of an integrally molded plastic coupling module 60 (numeral 130 in FIGS. 4(a) through 4(c) hereof) is that a not insignificant amount of undesirable EMI is generated inside such a module 60 (numeral 130 in FIGS. 4(a) through 4(c) hereof, and cannot be remedied merely by providing an X2 housing 200 formed of metal. Moreover, because component 60 (numeral 130 in FIGS. 4(a) through 4(c) hereof) is formed of plastic, providing cost-effective EMI shielding of such a component presents particular challenges. For example, sputtering, vapor-depositing or electro-plating such plastic components is difficult, time-consuming and expensive. Shielding such plastic components with overlying physical components such as wire shielding is also expensive, and additionally consumes excessive volume within the already small interior volume of X2 housing 200.
What is needed is a means of providing EMI shielding for substantially optically transparent or transmissive components, be they glass or plastic) in LX4 ROSAs and TOSAs, as well as in similar or like devices, that is functionally effective, amenable for use with plastic or glass, and that requires the use of minimal additional volume inside an X2 or other housing.
Various patents containing subject matter relating directly or indirectly to the field of the present invention include, but are not limited to, the following.
U.S. Pat. No. 5,777,856 to Phillips et al. for “Integrated Shielding and Mechanical Support,” Jul. 7, 1998.
U.S. Pat. No. 6,201,908 to Grann for “Optical Wavelength Division Multiplexer/Demultiplexer Having Preformed Passively Aligned Optics,” Mar. 13, 2001.
U.S. Pat. No. 6,206,582 to Gilliland for “EMI Reduction for Optical Subassembly,” Mar. 27, 2001.
U.S. Pat. No. 6,396,978 to Grann for “Optical Wavelength Division Multiplexer/Demultiplexer Having Patterned Opaque Regions to Reduce Optical Noise,” May 28, 2002.
U.S. Pat. No. 6,456,757 to Kim et al. for “Optical Wavelength Division Multiplexer/Demultiplexer Having Adhesive Overflow Channels with Dams to Achieve Tight Adhesive Bond,” Sep. 24, 2002.
U.S. Pat. No. 6,529,306 to Engel et al., for “Electromagnetic Interference Reduction Method and Apparatus,” Mar. 4, 2003.
U.S. Pat. No. 6,558,046 to Griffis et al. for “Optical Wavelength Division Multiplexer/Demultiplexer with Mechanical Strain Relief” May 6, 2003.
U.S. Pat. No. 6,563,976 to Grann et al. for “Cost-Effective Wavelength Division Multiplexer and Demultiplexer,” May 13, 2003.
U.S. Pat. No. 6,572,278 to Hsieh et al. for “Opto-Electronic Device Having Staked Connection between Parts to Prevent Differential Thermal Expansion,” Jun. 3, 2003.
U.S. Pat. No. 6,607,308 to Dair et al. for “Fiber-Optic Modules with Shielded Housing/Covers Having Mixed Finger Types,” Aug. 19, 2003.
U.S. Pat. No. 6,780,053 to Yunker et al. for “Pluggable Small-Form Factor Transceivers,” Aug. 24, 2004.
U.S. Pat. No. 6,781,693 to Richard et al. for “System and Method for Optical Multiplexing and/or Demultiplexing,” Aug. 24, 2004.
U.S. Pat. No. 6,816,646 to Nakama et al. for “Light-Sensitive Detector and Optical Demultiplexer,” Nov. 9, 2004.
U.S. Pat. No. 6,866,544 to Casey et al., for “Methods and Apparatus for Mounting an Electromagnetic Interference Shielding Cage to a Circuit Board,” Mar. 15, 2005.
U.S. Pat. No. 6,854,894 to Yunker et al. for “Optical Receptacle, Transceiver and Cage,” Feb. 15, 2005.
U.S. Pat. No. 6,856,722 to Sasaki et al. for “Optical Demultiplexer and Optical Multiplexer for wavelength Division Multiplex Communication,” Feb. 15, 2005.
U.S. Pat. No. 7,044,791 to Wang for “Shielded Optical-Electric Connector,” May 16, 2006.
U.S. Pat. No. 7,135,643 to van Haaster et al. for “EMI Shield Including a Lossy Medium,” Nov. 14, 2006.
U.S. Pat. No. 7,150,653 to Mason for “Techniques for EMI Shielding of a Transceiver Module,” Dec. 19, 2006.
U.S. Pat. No. 7,184,621 to Zhu for “Multi-Wavelength Transmitter Optical Sub Assembly with Integrated Multiplexer,” Feb. 27, 2007.
The dates of the foregoing publications may correspond to any one of priority dates, filing dates, publication dates and issue dates. Listing of the above patents and patent applications in this background section is not, and shall not be construed as, an admission by the applicants or their counsel that one or more publications from the above list constitutes prior art in respect of the applicant's various inventions.
Upon having read and understood the Summary, Detailed Description and Claims set forth below, those skilled in the art will appreciate that at least some of the systems, devices, components and methods disclosed in the printed publications listed herein may be modified advantageously in accordance with at least some of the teachings of the various embodiments of the present invention.